ATtiny167-ESSZ datasheet(72/282 Pages) ATMEL

72 / 282 page

7728D–AVR–07/09

ATtiny87/ATtiny167

9.2.6

Digital Input Enable and Sleep Modes

As shown in Figure 9-2, the digital input signal can be clamped to ground at the input of the

Schmitt Trigger. The signal denoted SLEEP in the figure, is set by the MCU Sleep Controller in

Power-down or Power-save mode to avoid high power consumption if some input signals are

left floating, or have an analog signal level close to Vcc/2.

SLEEP is overridden for port pins enabled as external interrupt pins. If the external interrupt

request is not enabled, SLEEP is active also for these pins. SLEEP is also overridden by vari-

ous other alternate functions as described in “Alternate Port Functions” on page 72.

If a logic high level (“one”) is present on an asynchronous external interrupt pin configured as

“Interrupt on Rising Edge, Falling Edge, or Any Logic Change on Pin” while the external inter-

rupt is not enabled, the corresponding External Interrupt Flag will be set when resuming from

the above mentioned Sleep mode, as the clamping in these sleep mode produces the

requested logic change.

9.2.7

Unconnected Pins

If some pins are unused, it is recommended to ensure that these pins have a defined level.

Even though most of the digital inputs are disabled in the deep sleep modes as described

above, floating inputs should be avoided to reduce current consumption in all other modes

where the digital inputs are enabled (Reset, Active mode and Idle mode).

The simplest method to ensure a defined level of an unused pin, is to enable the internal

pull-up. In this case, the pull-up will be disabled during reset. If low power consumption during

reset is important, it is recommended to use an external pull-up or pull-down. Connecting

unused pins directly to Vcc or GND is not recommended, since this may cause excessive cur-

rents if the pin is accidentally configured as an output.

9.3

Alternate Port Functions

Most port pins have alternate functions in addition to being general digital I/Os. Figure 9-6

shows how the port pin control signals from the simplified Figure 9-2 can be overridden by

alternate functions. The overriding signals may not be present in all port pins, but the figure

serves as a generic description applicable to all port pins in the AVR microcontroller family.

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